The effect of combined respiratory and nonrespiratory alkalosis on energy metabolites and acid-base parameters in the rat brain

Recurrent metabolic alkalosis and elevated troponins after crack cocaine use in a hemodialysis patient

When acid-base disorders have been described after cocaine use, they are usually metabolic acidosis. We report a case of recurrent crack cocaine use associated with severe metabolic alkalosis on two successive admissions, in a patient in renal failure on hemodialysis and with minimal urine output, despite no history of vomiting or alkali ingestion. The metabolic alkalosis did not recur after counseling and abstention from cocaine.

Protection of focal cerebral ischemia by alkalinization of systemic pH

OBJECT

It has been demonstrated in many studies that intracellular brain acidosis during cerebral ischemia is a significant factor in perpetuating the cycle of cellular dysfunction leading to neuronal injury. The purpose of this study was to determine whether preischemic administration of alkalotic agents could reduce neuronal injury after focal cerebral ischemia.

METHODS

Fifteen fasted rabbits under 1.0% halothane anesthesia were randomized into three groups: Group 1 rabbits were ischemic controls (n = 5) that underwent 4 hours of focal cerebral ischemia. Groups 2 and 3 rabbits underwent a paradigm similar to that of Group 1, except that they were pretreated with either sodium bicarbonate or Carbicarb at similar buffering capacities. Intracellular brain pH (pH(i)), regional cortical blood flow (rCBF), and intrinsic reduced nicotinamide adenine dinucleotide (NADH) fluorescence were measured with in vivo fluorescence imaging. At the end of each experiment, infarct volume expressed as a percentage of hemispheric volume was measured by triphenyltetrazolium chloride staining.

RESULTS

Preischemic alkalinization did not alter brain pH(i), rCBF, or NADH fluorescence. After 4 hours of ischemia, brain pH(i), rCBF, NADH fluorescence, and infarct volume measured 6.40 +/- 0.09 (mean +/- standard error), 11 +/- 2 ml/100 g/min, 165 +/- 8% of baseline control, and 37 +/- 3% in ischemic controls, respectively. In Group 2 animals treated with sodium bicarbonate, brain pH(i), rCBF, NADH fluorescence, and infarct volume improved significantly (P < 0.05, analysis of variance) to 6.74 +/- 0.08, 24 +/- 6 ml/100 g/min, 137 +/- 6% of baseline control, and 22 +/- 4%, respectively. Group 3 Carbicarb animals demonstrated improvements in brain pH(i), rCBF, and NADH fluorescence, with a significant reduction in infarct volume.

CONCLUSION

These findings suggest that pretreatment with alkalinizing agents may be a useful intervention to provide intraoperative cerebral protection from ischemic injury.

The effect of metabolic acidosis and alkalosis on the H+-ATPase of rat cerebral microvessels

To determine the role of the proton translocating adenosine triphosphatase (H+-ATPase) of the blood-brain barrier, the density of the 31 Kd subunit of the vacuolar type H+-ATPase was quantitated in isolated rat cerebral microvessels with immunoblotting techniques. To establish the tissue specificity of the findings, synaptosomal membranes were also studied. Metabolic acidosis was induced with 1.5% ammonium chloride in drinking water for five days. Metabolic alkalosis was induced with 2.35% NaHCO3 in drinking water and daily injections of 10 mg/Kg furosemide intraperitoneally for 5 days. The quantity of the 31 Kd subunit (in arbitrary units) in cerebral microvessels was significantly increased in acidosis (3.98 +/- 0.45) (p<0.05) and was significantly decreased in metabolic alkalosis (0.49 +/- 0.16) (p<0.00) compared to controls (1.77 +/- 0.73). In synaptosomal membranes, metabolic alkalosis was associated with significant decrease in the quantity of the 31 Kd subunit-H+-ATPase (0.62 +/- 0.12 vs 0.92 +/- 0.01) p<0.05. The increase in the 31 Kd subunit in synaptosomal membranes with acidosis did not reach statistical significance. It is concluded that the quantity of vacuolar H+-ATPase in the blood-brain barrier is modulated by blood H+ or HCO3- content. These changes may be relevant to the physiology of the acid-base balance in the central nervous system.

Hypocapnia and cerebral ischaemia in hypotensive newborn piglets

This study tested the hypothesis that hypocapnia superimposed upon hypotension produces a further reduction in cerebral blood flow velocity (CBFV). In 12 newborn piglets, CBFV was measured continuously by Doppler ultrasound through an artificial fontanelle. Hypotension was induced by removing 30 ml/kg of blood. Increasing the ventilator rate reduced the average arterial carbon dioxide tension from 5.5 to 2.0 kPa. When mean arterial pressure (MAP) was held steady at 45 mm Hg or above, hypocapnia produced a substantial drop in CBFV but, in all the piglets with MAP below 38 mm Hg, hypocapnia failed to change CBFV by 10%. Hypocapnia produced an increase in lactate in sagittal sinus blood but cerebral venous hypoxanthine concentrations were not affected by hypocapnia. Hyperventilation (without haemorrhage) produced a significant drop in MAP, preventable by infusing colloid. Hypocapnia itself does not further reduce CBFV in the hypotensive piglet. However, the pressure effect of hyperventilation may significantly impair the cerebral circulation.

1H and 31P NMR measurement of cerebral lactate, high-energy phosphate levels, and pH in humans during voluntary hyperventilation: associated EEG, capnographic, and Doppler findings

In order to explore the sensitivity of spatially resolved 1H and 31P NMR spectroscopy on a whole-body NMR instrument, cerebral metabolic changes in human volunteers were measured during hyperventilation provocation. During hyperventilation the flow velocity in the middle cerebral artery decreased significantly and the EEG showed a marked increase in slow activity. 1H NMR spectra revealed an increase in cerebral lactate concentration. 31P NMR spectra showed no changes in ATP or PCr peak heights, but a shift toward tissue alkalosis was derived from changes in Pi chemical shift. During subsequent recovery, lactate concentration decreased and a slight intracellular acidosis was detected. In three experiments broadening of the lactate resonance peak resulted in separation into two components at 1.32 and 1.48 ppm, in which the latter signal possibly arose from alanine.

The young-adult and normally aged brain. Its blood flow and oxidative metabolism. A review--part I

Blood flow and oxidative metabolism of the mature and healthy young-adult human brain account for about 20% of the cardiac output and about 20 and 25% of the requirements of oxygen and glucose, respectively, for the whole body. Normal cerebral aging is associated with only smaller reductions in the cerebral metabolic rates of oxygen and glucose while cerebral blood flow would seem to be unchanged. The age-dependent reduction in oxidative brain metabolism may be related to a decline in glycolytic flux due to a diminution of enzyme activities also involving acetylcholine synthesis. This metabolic reduction with age may be tentatively accounted for by a physiologically occurring loss of neurons, dendrites and dendritic spines in distinct brain areas. The mechanisms of autoregulation of cerebral blood flow, of CO2 reactivity of the brain vessels, of arterial hypoxemia on cerebral blood flow and their effects on oxidative and energy metabolism are well documented in young-adult brain. There is, however, no or only minimal information on the responsiveness of the normally aged brain to changes of these important biological parameters controlling and influencing brain blood flow and metabolism.

Effects of severe arterial hypocapnia on regional blood flow regulation, tissue PO2 and metabolism in the brain cortex of cats

The effect of a stepwise decrease in PaCO2 from 3.9-1.6 kPa on rCBF, rCMRO2, tissue PO2 and concentrations of glucose, lactate, pyruvate, ATP, ADP, AMP and phosphocreatine in the brain cortex was studied in cats lightly anaesthetized with sodium pentobarbital. 1. Moderate lowering of PaCO2 to 2.5 kPa induced in all animals a homogeneous decrease of rCBF in corresponding areas of the right and left hemisphere. Mean rCBF fell from 129.2 to 103.1 ml X 100 g-1 X min-1, while rCMRO2 remained unchanged (12.7-12.9 ml X 100 g-1 X min-1). The tissue PO2 frequency histograms showed a shift to lower values without indicating the presence of brain tissue hypoxia. 2. Severe arterial hypocapnia (PaCO2 = 1.6 kPa) caused an inhomogeneous blood flow reaction. Both further decreased as well as increased rCBF values were measured simultaneously in the brain cortex of individual animals (mean rCBF = 97.6 ml X 100 g-1 X min-1). At the same time tissue PO2 measurements and metabolite assays indicated the presence of pronounced brain tissue hypoxia. The tissue concentrations of lactate and pyruvate and the lactate/pyruvate ratio were significantly increased, while the phosphocreatine concentration was significantly reduced. In addition, rCMRO2 decreased to 11.3 ml X 100 g-1 X min-1. The results provide conclusive evidence that severe arterial hypocapnia leads to an insufficient O2 supply of the brain cortex, which in turn seems to counteract the influence of hypocapnia on cortical blood flow regulation.

Effect of non-respiratory alkalosis on brain tissue and cerebral blood flow in rats with damaged blood-brain barrier

Acute alterations in plasma bicarbonate concentration have minimal effects on intracerebral pH and cerebral blood flow, perhaps due to blood-brain barrier mechanisms. To test this hypothesis, the consequences of an acute rise in the plasma bicarbonate concentration were studied in anesthetized rats previously subjected to an acute pressure pulse in the carotid system with unilateral damage to the blood-brain barrier. In rats subjected to a "heavy" hypertensive insult, the hemisphere on the side of the lesion showed a lactic acidosis, edema, and a depression of cerebral blood flow. An increase in the plasma bicarbonate concentrations of 15--20 mEq/1 during 35 minutes provoked a marked rise in the total CO2 content of this hemisphere, and a further increase in the lactate concentration, but did not later the brain edema nor affect further the already very low cerebral blood flow. An increase in the lactate concentration and a decrease of cerebral blood flow in the "reference" hemisphere indicated that the lesion was not completely unilateral. In rats subjected to a "moderate" hypertensive insult the changes were less pronounced and statistically not significant for all the parameters. There results illustrate the importance of an intact blood-brain barrier for the maintenance of intracerebral pH in the face of acute alterations in plasma [HCO3]. The impaired cerebral blood flow after an acute hypertensive insult did not appear to be influenced by the intracerebral [HCO3].